Melatonin has been suggested as a potent antioxidant that may protect against development of atherosclerosis and cancer; however, these effects are unproven and controversial. The antioxidant capacity of melatonin was tested in comparison with α-tocopherol, ascorbic acid, and the melatonin precursors tryptophan and serotonin, by measuring inhibition of metal ion-mediated and human macrophage-mediated oxidation of LDL. Melatonin had weak antioxidant activity that was detectable only at concentrations 10 000- to 100 000-fold higher than physiologic concentrations. These results were comparable with published data showing that the radical scavenging activity of melatonin requires markedly supraphysiologic concentrations. In contrast, α-tocopherol was 50- to 100-fold more potent and was efficacious at physiologic concentrations. Ascorbic acid and tryptophan also were active at physiologic concentrations and were significantly more potent than melatonin. In summary, extremely supraphysiologic concentrations of melatonin had only weak antioxidant activity, which was surpassed by α-tocopherol, ascorbic acid, and tryptophan.

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A patient with sickle cell disease who concomitantly developed red cell autoimmunity and alloimmunization is reported. The implied but 'wrong' specificity of the autoantibody mimicked one of the alloantibodies in the patient's serum. Although the patient's red blood cells phenotyped at Ro4, anti-rh" was eluted from them on several occasions. Absorption and secondary elution from selected cells proved the cell bound antibody had a unique and independent specificity from the anti-rh" in his serum. Standard antibody identification procedures did not distinguish these differences.

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